Conventionally, a workpiece (e.g. a tape, a substrate, or a strip) is held by vacuum to a chuck table during a cutting process. The chuck table can provide forward, backward, and rotational motion. In particular, the chuck table can move forward so that the rotating blade(s) of a cutting device on top of the workpiece cuts the workpiece that is placed on the chuck table. After cutting of the workpiece is completed in a first direction, a positioning device (e.g. a theta motor or a belt driven by an external rotary motor) rotates the chuck table by 90 degrees, so that cutting of the workpiece can be performed in a second direction that is perpendicular to the first direction. In this way, the workpiece can be cut by the cutting device to obtain an array of smaller units.
In the case of a workpiece that is held to the chuck table via a tape, the top side of the tape comprises a layer of adhesive for holding the workpiece, while vacuum from the chuck table holds the tape from its bottom side. Due to the soft and thin (less than 0.5 mm) nature of the tape, gaps between the chuck table and tape can be sealed up to prevent vacuum leakage. This ensures that the workpiece is firmly held to the chuck table via the tape, so that the workpiece can be accurately cut by the cutting device.
In contrast, holding a workpiece onto the chuck table by vacuum via a rubber jig is more difficult than via the tape. First, warpage of the workpiece due to internal stress within the workpiece coupled with the absence of an adhesive layer at the top side of the rubber jig may result in the presence of micro gaps between the rubber jig and the workpiece. Secondly, the rubber jig is harder and thicker than the tape and thus, micro gaps may also exist between the chuck table and the rubber jig. Consequently, the presence of micro gaps would compromise the stability of the workpiece during the cutting process. Vibration of the workpiece during the cutting process further increases the likelihood of chipping and damage of the workpiece.
FIG. 1a shows a conventional singulation apparatus 100 comprising: i) a chassis 109; ii) a rotary chuck table 110 rotatable relative to the chassis 109, the chuck table 110 being operative to hold a workpiece 104 thereto via a rubber jig 106; and iii) a cutting device 103 with rotating blades 105 for cutting the workpiece 104. In order to provide vacuum for holding the workpiece 104 to the chuck table 110, a plurality of vacuum tubes 108 are connected to vacuum holes 111 of the chuck table 110 and housed within an interior compartment of the chassis 109. During operation, the vacuum tubes 108 are capable of bending and twisting as the chuck table 110 moves linearly and/or rotates relative to the chassis 109.
FIG. 1b shows another conventional singulation apparatus 120 that is similar to the singulation apparatus 100 shown in FIG. 1a. Like the singulation apparatus 100, the singulation apparatus 120 comprises: i) a chassis 129; ii) a rotary chuck table 130 rotatable relative to the chassis 129, the chuck table 130 being operative to hold a workpiece 124 thereto via a rubber jig 126; iii) a cutting device 123 having rotating blades 125 for cutting the workpiece 124; and iv) a plurality of vacuum tubes 128 connected to vacuum holes 121 of the chuck table 130. In contrast with the singulation apparatus 100 of FIG. 1a, however, the vacuum tubes 128 of the singulation apparatus 120 of FIG. 1b are located at an exterior and not within an interior compartment of the chassis 129.
The quantity of the vacuum tubes 108, 128 in the singulation apparatus 100, 120 should thus be limited. Otherwise, the positioning device that rotates the chuck table 110, 130 cannot provide enough torque to overcome torsion forces created by the twisted vacuum tubes 108, 128. Moreover, the requirement to have sufficient space for storing the vacuum tubes 108, 128 that connect to the vacuum holes of the chuck table 110 also presents a further constraint. As the vacuum force increases proportionally with the total number of vacuum tubes 108, 128, the vacuum force created in the singulation apparatus 100, 120 may not be strong enough to hold the workpiece firmly during cutting. Consequently, the workpiece may vibrate during operation, which increases the likelihood of damage to the workpiece and/or the cutting blade during operation.
Thus, it is an object of the present invention to propose an apparatus and method for supporting a workpiece during processing that address the problems faced by conventional apparatus as described above.